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The aim of thyroid hormone treatment post-TT for cancer always seems to be to suppress TSH.

I have NO understanding of whether high T3 (relatively) could impact on cancer cells, but if the general idea "suppressing TSH is a good thing" is right, then perhaps it makes little difference how that is achieved - by T4 or by T3?

....thanks Rod - yes I agree it would be. If T3 works at a cellular level to speed things up - then the last thing we would want for anyone is to speed production of the rogue cells. My simplistic thinking comes from what I have read over the years that cancers are slow growing in older people when their cell renewal has slowed down......possibly due to lowered metabolism I now realise.